Start with the result
Before asking for proposals, describe what work should become better after the project. Not only a feature list, but a real operating result: less manual work, more reliable data, faster orders, clearer reporting.
A supplier who understands the outcome will ask more uncomfortable questions. That is usually a good sign.
Compare more than price
Evaluate scope, assumptions, data migration, integrations, testing, training, responsibilities and post-go-live support.
The cheapest proposal is often cheapest because part of the work is missing or moved to a vague later phase.
What to watch in a demo
A useful demo should use your data, your process and your edge cases. If the demo only shows a polished standard environment, project risk has not yet been tested.